The present invention relates generally to DC-DC converters and voltage regulators, and more particularly to very low power implementations thereof that are especially adapted for use in conjunction with energy harvesters.
FIG. 1 shows a conventional DC-DC converter or LDO (low drop out) voltage regulator 1 including a voltage reference circuit 3 which applies a reference voltage VREF to the (−) input of an error amplifier 2. Voltage reference 3 typically is a 1.2 volt bandgap circuit. Output 2A of error amplifier 2 is connected to the input of an output stage 4. Output stage 4 produces an output voltage VOUT on conductor 5, which is connected to one terminal of a load 6. The other terminal of load 6 is connected to ground. A resistive voltage divider circuit including series-connected resistors R0 and R1 is connected between VOUT and ground. The junction between resistors R0 and R1 is coupled by conductor 7 to the (+) input of error amplifier 2. Error amplifier 2 and output stage 4 are coupled between VDD and ground.
The voltage regulation loop of DC-DC converter or LDO voltage regulator 1 includes output stage 4, error amplifier 2, voltage reference 3, and resistive voltage divider R0,R1. Resistive voltage divider R0,R1 sets the desired value of the DC output voltage VOUT and allows the value of VOUT to be set to a level below, equal to, or above VREF. Resistors R0 and R1 usually are external resistors mounted on a printed circuit board along with an integrated circuit chip including the other components of DC-DC converter 1. External resistors R0 and R1 typically have values of no more than about 1 to 2 megohms, because of leakage currents in the printed circuit board. If resistors R0 and R1 are formed on the integrated circuit chip, then they are expensive because of the large amount of chip area occupied by them. In either case, the power dissipation in the feedback resistor network R0,R1 is dominant if very low-power circuitry that is commonly referred to as “nano-power” circuitry is used to implement error amplifier 2 and output stage 4 in extremely low-power applications such as energy harvester systems.
In low power applications, the typical several microampere current through resistor divider R0,R1 is a substantial or even major part of the overall current consumed by the DC-DC converter or LDO voltage regulator 1 and therefore substantially diminishes the efficiency of converter 1 at small load currents of a few microamperes or less.
By way of definition, the term “DC-DC converter” as used herein is intended to encompass various kinds of DC-DC converters such as boost converters, buck converters, and buck/boost converters, and also is intended to encompass LDO voltage regulators. Also by way of definition, the term “nano-power” as used herein is intended to encompass circuits and/or circuit components which draw DC current of less than approximately 1 microampere.
Various low-power error amplifier configurations are known, and subsequently described Prior Art FIG. 6 shows a known low power error amplifier.
Thus, there is an unmet need to provide a way of substantially reducing the current and power consumption of a DC-DC converter.
There also is an unmet need for a DC-DC converter of the kind having a voltage divider feedback network that consumes only a minute average amount of current and power.
There also is an unmet need for a DC-DC converter of the kind having a voltage divider feedback network that consumes less than approximately 5 microamperes of current.